“…On the contrary, the ultrasonic method is widely employed for wall thickness inspections due to its advantages of [4,5]: being nonhazardous and applicable for thickness measurements of thick material, the detection of discontinuity, and the determination of material properties. However, the ultrasonic thickness measurement (UTM) is based on measuring the transit time that is required for a short ultrasonic pulse to travel through the material once, twice, or several 2 of 15 times, which leads to the need for the UTM system to know the precise physical characteristics, such as the ultrasonic velocity, going through the material [6]. Therefore, often authors investigate and develop new methods for determining ultrasonic velocity [7,8], but usually they present measurement results without the associated measurement uncertainty.…”